1. Field of the Invention
This invention relates to monitors for Sudden Infant Death Syndrome (SIDS) and, in particular, relates to SIDS monitors configured to minimize false alarm problems from, for example, motion artifacts.
2. Description of the Prior Art
Sudden infant death syndrome is the medical terminology used to designate the almost inexplicable deaths of seemingly healthy infants. Commonly known as crib death, SIDS is the leading category of infant deaths between the ages of two weeks and one year and account for one-third of all deaths after the new born period.
Despite limited information, a scientific consensus suggests that SIDS occurred in healthy infants as a result of the simultaneous occurrence of a series of seemingly unrelated biological events. Infants who have periods of apnea, or difficulty in breathing, sudden skin color change to blue or pale, changes in muscle tone either to limpness or rigidity and who appear to require help in breathing are more likely to die of SIDS. These episodes can occur during sleep, feeding or while awake and are now known as apparent life-threatening events or ALTEs.
Specially designed apnea/bradycardia alarm systems became available for home use in the late 1970s to monitor infant breathing in an attempt to reduce SIDS. Conventional apnea/bradycardia monitors use electrodes attached to the infant's skin. The monitors provide an audible alarm if the baby stops breathing for a pre-determined period of time, or when the heart rate drops below a designated level, to indicate to the parent or guardian that the baby may need assistance in breathing. Conventional home monitors may now also include means for recording the electrocardiogram and respiratory wave form before, during or after the alarm event.
A number of scientific studies find a significant reduction in the incidence of SIDS in high risk groups utilizing home monitoring programs. However, conventional SIDS monitors are subject to many false alarms making it difficult for parents to maintain their watchfulness. The causes of such false alarms depends upon the type of monitor used. Transthoracic impedance based cardiorespiratory monitors, for example, are susceptible to cardiogenic artifacts. The resultant large number of false alarms, estimated to be on the order of 5 to 7 false alarms per monitoring period, substantially increases parental anxiety and therefore unfortunately reduces the likelihood that successful monitoring will be properly performed on a long term basis.
The pulse oximeter has been suggested for use as a SIDS monitor to monitor the blood hemoglobin oxygen saturation as a means of detecting hypoxemia secondary to apnea and hypoventilation as oxygen desaturation is the first event to occur in Sudden Infant Death Syndrome.
Conventional oxygen saturation monitors measure a light signal passed through an extremity that determines the wave length change created by oxygen containing red blood cells. Saturation probes are typically placed on the fingers, toes, hands or feet of the infant. Probe position on the infant's extremities therefore makes saturation measurements particularly susceptible to motion artifacts caused by movement of the infant. Positioning the probe electrodes on the infant's sternum or back has been proposed in an attempt to reduce the effects of infant movement.
In addition, various motion artifact compensating devices, such as accelerometers, have been developed for use with pulse oximeters used for other purposes. Unfortunately, motion artifacts still cause so many false alarms that the use of home oxygen saturation monitors is as frustrating to parents as other monitors even though oxygen saturation measurements hold out a substantial promise for reducing SIDS.
The integration of saturation monitoring with respiratory and cardiac monitoring has been also proposed. Nasal airflow, detected for example with a thermistor in the airflow path, are well known. Other types of respiratory measurements, not requiring the placement of a probe in the nasal passageway, have been developed to reduce the practical difficulties and inconvenience of the respiratory probe location.
Because of the high false alarm rate, the lack of clear understanding of the causes of SIDS and the resultant confusion about the most appropriate conditions to be monitored, physicians and parents have no clear path to pursue for protection. All that is really clear is that, when properly monitored, high risk infants have a better chance of survival.
What are needed are monitoring techniques that substantially increase the number of infants properly monitored and reduce the occurrence of false alarms in SIDS monitoring.